382 i Flora Unveiled
for centuries in the form of literary conceits. For example, in Sonnet 15, Shakespeare utilized
a human– plant analogy to universalize the corrosive effects of time and compares his own
sonnets praising his friend to freshly grafted scions, which renew the life of an aging stock:
When I consider every thing that grows
Holds in perfection but a little moment,
That this huge stage presenteth nought but shows
Whereon the stars in secret influence comment;
When I perceive that men as plants increase,
Cheered and cheque’d even by the self- same sky,
Vaunt in their youthful sap, at height decrease,
And wear their brave state out of memory;
Then the conceit of this inconstant stay
Sets you most rich in youth before my sight,
Where wasteful Time debateth with Decay,
To change your day of youth to sullied night;
And all in war with Time for love of you,
As he takes from you, I engraft you new.By the eighteenth century, plant– human analogies had become respectable in scien-
tific circles as well. Mettrie had been thunderstruck by the 1744 publication of Abraham
Trembley’s experiments on regeneration in Hydra.^10 It was common knowledge that entire
plants could be propagated from cuttings, and it was also known that certain animals,
such as starfish, crayfish, and lizards, could regenerate lost appendages. But a severed lizard
tail would never regenerate a whole lizard, nor a crayfish leg regenerate a whole crayfish.
According to Aristotle, cutting an animal in half invariably killed it, whereas cutting a
plant in half did not, a distinction he attributed to the multiplicity of plant souls.
In the course of examining drops of lake water under a microscope, Trembley encoun-
tered an organism previously described by Leeuwenhoek, the freshwater polyp, or Hydra,
which typically ranges in size from 2 to 10 mm. Because the tiny polyp was green (due to
the presence of algae) he initially thought it was a plant, but as it seemed to be able to move
about and even capture food with its tentacles he decided it must be an animal. Applying
Aristotle’s criterion, he carefully snipped the hydra in half transversely with a scissors to
see if would survive. At first the two halves (head and tail) each contracted into a little
green ball, but they soon re- extended to their normal shapes. Several days later, the half that
contained the head regenerated its bottom half. Trembley wasn’t too surprised by this since
lizards also regenerated their tails. But when the tail end of the hydra regenerated a head, he
was astounded. If he cut the Hydra lengthwise into quarters, each piece regenerated a com-
plete organism, although further subdivisions resulted in death. Trembley subsequently
found that when he bisected the head longitudinally, the two halves each regenerated a
complete head. Using this trick, he was able to produce a seven- headed Hydra.^11
Upon reading Trembley’s report, Mettrie realized that Aristotle’s blanket distinction
between plants and animals was false. It was evident to him that the border between plants
and animals consisted of intermediate organisms that had features of both kingdoms.
Plants, animals, and even humans were all part of a continuum. Thus he felt justified in
comparing men and women to dioecious plants.